Hash-based remote rebuild assistance for content addressable storage systems

ABSTRACT

An apparatus in an illustrative embodiment comprises at least one processing device comprising a processor coupled to a memory. The processing device detects a drive failure in a first storage system comprising a plurality of drives configured in accordance with a designated redundant array of independent disks (RAID) arrangement, identifies a plurality of data pages to be rebuilt in order to recover from the drive failure, retrieves hash digests of respective ones of the identified data pages, and utilizes the hash digests to request respective corresponding data pages from a second storage system. For each of one or more data pages returned by the second storage system, the processing device utilizes the returned data page as a rebuilt data page in recovering from the drive failure so as to avoid reading multiple data pages from remaining ones of the drives of the designated RAID arrangement to rebuild that data page.

FIELD

The field relates generally to information processing systems, and moreparticularly to storage in information processing systems.

BACKGROUND

Various types of content addressable storage systems are known. Somecontent addressable storage systems allow data pages of one or morelogical storage volumes to be accessed using content-based signaturesthat are computed from content of respective ones of the data pages.Such content addressable storage system arrangements facilitateimplementation of deduplication and compression. For example, thestorage system need only maintain a single copy of a given data pageeven though that same data page may be part of multiple logical storagevolumes. Although these and other content addressable storage systemstypically provide a high level of storage efficiency throughdeduplication and compression, problems can arise under certainconditions. For example, a failure occurring in a given storage drive ofa content addressable storage system that implements a redundant arrayof independent disks (RAID) arrangement will typically require atime-consuming and computationally-intensive rebuild process. Inaddition, the content addressable storage system is operating in avulnerable state during the rebuild process, as any additional drivefailures arising while the rebuild process is underway can cause actualdata loss.

SUMMARY

Illustrative embodiments provide techniques for hash-based remoterebuild assistance that facilitate recovery from drive failures in afirst storage system. In some embodiments, the first storage system isconfigured to participate in a replication process with a second storagesystem, with the first and second storage systems illustrativelycomprising respective content addressable storage systems. Thehash-based remote rebuild assistance techniques can advantageously avoidrebuilding certain data pages of a failed drive by instead using theirexisting hash digests in the first storage system to recover thecorresponding data pages from the second storage system. As a result,such arrangements significantly reduce the amounts of time andcomputational resources that would otherwise be required in the rebuildprocess. The hash-based remote rebuild assistance also advantageouslyreduces the vulnerability of the first storage system to actual dataloss by reducing the time required to complete the rebuild process.

In one embodiment, an apparatus comprises at least one processing devicecomprising a processor coupled to a memory. The processing device isconfigured to detect a drive failure in a first storage systemcomprising a plurality of drives configured in accordance with adesignated RAID arrangement, to identify a plurality of data pages to berebuilt in order to recover from the drive failure, to retrieve hashdigests of respective ones of the identified data pages, and to utilizethe hash digests to request respective corresponding data pages from asecond storage system, such as, for example, a second storage systemconfigured to participate in a replication process with the firststorage system. Other types of relationships are possible between thefirst and second storage systems, and replication is not required.

For each of one or more data pages returned by the second storagesystem, the processing device is further configured to utilize thereturned data page as a rebuilt data page in recovering from the drivefailure so as to avoid reading multiple data pages from remaining onesof the drives of the designated RAID arrangement to rebuild that datapage.

The processing device in some embodiments is implemented in a hostdevice configured to communicate over a network with the first andadditional storage systems. In other embodiments, the processing deviceis implemented in the first storage system. These are only examples, andalternative implementations are possible.

The first storage system in some embodiments comprises a clusteredimplementation of a content addressable storage system having adistributed storage controller. The content addressable storage systemin arrangements of this type is illustratively configured to utilizenon-volatile memory storage devices, such as flash-based storagedevices. For example, the storage devices of the first storage system insuch embodiments can be configured to collectively provide an all-flashstorage array. Numerous other storage system arrangements are possiblein other embodiments.

These and other illustrative embodiments include, without limitation,apparatus, systems, methods and processor-readable storage media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an information processing system comprisinga content addressable storage system configured to implement hash-basedremote rebuild assistance in an illustrative embodiment.

FIG. 2 illustrates a portion of a distributed storage controller of acontent addressable storage system showing one possible arrangementutilizing control modules and data modules interconnected by a meshnetwork and configured to implement hash-based remote rebuild assistancein an illustrative embodiment.

FIG. 3 is a flow diagram showing a process for implementing hash-basedremote rebuild assistance in an illustrative embodiment.

FIGS. 4A, 4B, 4C and 4D show examples of logical layer and physicallayer mapping tables in an illustrative embodiment.

FIGS. 5 and 6 show examples of processing platforms that may be utilizedto implement at least a portion of an information processing system inillustrative embodiments.

DETAILED DESCRIPTION

Illustrative embodiments will be described herein with reference toexemplary information processing systems and associated computers,servers, storage devices and other processing devices. It is to beappreciated, however, that these and other embodiments are notrestricted to the particular illustrative system and deviceconfigurations shown. Accordingly, the term “information processingsystem” as used herein is intended to be broadly construed, so as toencompass, for example, processing systems comprising cloud computingand storage systems, as well as other types of processing systemscomprising various combinations of physical and virtual processingresources. An information processing system may therefore comprise, forexample, at least one data center or other cloud-based system thatincludes one or more clouds hosting multiple tenants that share cloudresources. Numerous different types of enterprise computing and storagesystems are also encompassed by the term “information processing system”as that term is broadly used herein.

FIG. 1 shows an information processing system 100 configured inaccordance with an illustrative embodiment. The information processingsystem 100 comprises a computer system 101 that includes host devices102-1, 102-2, . . . 102-N. The host devices 102 communicate over anetwork 104 with a content addressable storage system 105. The contentaddressable storage system 105 is an example of what is more generallyreferred to herein as a “storage system,” and it is to be appreciatedthat a wide variety of other types of storage systems can be used inother embodiments.

The host devices 102 and content addressable storage system 105illustratively comprise respective processing devices of one or moreprocessing platforms. For example, the host devices 102 and the contentaddressable storage system 105 can each comprise one or more processingdevices each having a processor and a memory, possibly implementingvirtual machines and/or containers, although numerous otherconfigurations are possible.

The host devices 102 and content addressable storage system 105 may bepart of an enterprise computing and storage system, a cloud-based systemor another type of system. For example, the host devices 102 and thecontent addressable storage system 105 can be part of cloudinfrastructure such as an Amazon Web Services (AWS) system. Otherexamples of cloud-based systems that can be used to provide one or moreof host devices 102 and content addressable storage system 105 includeGoogle Cloud Platform (GCP) and Microsoft Azure.

The host devices 102 are configured to write data to and read data fromthe content addressable storage system 105. The host devices 102 and thecontent addressable storage system 105 may be implemented on a commonprocessing platform, or on separate processing platforms. A wide varietyof other types of host devices can be used in other embodiments.

The host devices 102 in some embodiments illustratively provide computeservices such as execution of one or more applications on behalf of eachof one or more users associated with respective ones of the host devices102.

The term “user” herein is intended to be broadly construed so as toencompass numerous arrangements of human, hardware, software or firmwareentities, as well as combinations of such entities. Compute and/orstorage services may be provided for users under a Platform-as-a-Service(PaaS) model, an Infrastructure-as-a-Service (IaaS) model and/or aFunction-as-a-Service (FaaS) model, although it is to be appreciatedthat numerous other cloud infrastructure arrangements could be used.Also, illustrative embodiments can be implemented outside of the cloudinfrastructure context, as in the case of a stand-alone computing andstorage system implemented within a given enterprise.

The network 104 is assumed to comprise a portion of a global computernetwork such as the Internet, although other types of networks can bepart of the network 104, including a wide area network (WAN), a localarea network (LAN), a satellite network, a telephone or cable network, acellular network, a wireless network such as a WiFi or WiMAX network, orvarious portions or combinations of these and other types of networks.The network 104 in some embodiments therefore comprises combinations ofmultiple different types of networks each comprising processing devicesconfigured to communicate using Internet Protocol (IP) or othercommunication protocols.

As a more particular example, some embodiments may utilize one or morehigh-speed local networks in which associated processing devicescommunicate with one another utilizing Peripheral Component Interconnectexpress (PCIe) cards of those devices, and networking protocols such asInfiniBand, Gigabit Ethernet or Fibre Channel. Numerous alternativenetworking arrangements are possible in a given embodiment, as will beappreciated by those skilled in the art.

The content addressable storage system 105 is accessible to the hostdevices 102 over the network 104. The content addressable storage system105 comprises a plurality of storage devices 106 and an associatedstorage controller 108. The storage devices 106 illustratively storemetadata pages 110 and user data pages 112. The user data pages 112 insome embodiments are organized into sets of logical units (LUNs) eachaccessible to one or more of the host devices 102. The LUNs may beviewed as examples of what are also referred to herein as logicalstorage volumes of the content addressable storage system 105.

The storage devices 106 illustratively comprise solid state drives(SSDs). Such SSDs are implemented using non-volatile memory (NVM)devices such as flash memory. Other types of NVM devices that can beused to implement at least a portion of the storage devices 106 includenon-volatile random access memory (NVRAM), phase-change RAM (PC-RAM) andmagnetic RAM (MRAM). These and various combinations of multipledifferent types of NVM devices may also be used.

However, it is to be appreciated that other types of storage devices canbe used in other embodiments. For example, a given storage system as theterm is broadly used herein can include a combination of different typesof storage devices, as in the case of a multi-tier storage systemcomprising a flash-based fast tier and a disk-based capacity tier. Insuch an embodiment, each of the fast tier and the capacity tier of themulti-tier storage system comprises a plurality of storage devices withdifferent types of storage devices being used in different ones of thestorage tiers. For example, the fast tier may comprise flash driveswhile the capacity tier comprises hard disk drives. The particularstorage devices used in a given storage tier may be varied in otherembodiments, and multiple distinct storage device types may be usedwithin a single storage tier. The term “storage device” as used hereinis intended to be broadly construed, so as to encompass, for example,flash drives, solid state drives, hard disk drives, hybrid drives orother types of storage devices.

In some embodiments, the content addressable storage system 105illustratively comprises a scale-out all-flash content addressablestorage array such as an XtremIO™ storage array from Dell EMC ofHopkinton, Mass. For example, the content addressable storage system 105can comprise an otherwise conventional XtremIO™ storage array or othertype of content addressable storage system that is suitably modified toincorporate hash-based remote rebuild assistance as disclosed herein.Other types of storage arrays, including by way of example VNX® andSymmetrix VMAX® storage arrays also from Dell EMC, can be used toimplement content addressable storage system 105 in other embodiments.

The term “storage system” as used herein is therefore intended to bebroadly construed, and should not be viewed as being limited to contentaddressable storage systems or flash-based storage systems. A givenstorage system as the term is broadly used herein can comprise, forexample, network-attached storage (NAS), storage area networks (SANs),direct-attached storage (DAS) and distributed DAS, as well ascombinations of these and other storage types, includingsoftware-defined storage.

Other particular types of storage products that can be used inimplementing content addressable storage system 105 in illustrativeembodiments include all-flash and hybrid flash storage arrays such asUnity™, software-defined storage products such as ScaleIO™ and ViPR®,cloud storage products such as Elastic Cloud Storage (ECS), object-basedstorage products such as Atmos®, and scale-out NAS clusters comprisingIsilon® platform nodes and associated accelerators, all from Dell EMC.Combinations of multiple ones of these and other storage products canalso be used in implementing a given storage system in an illustrativeembodiment.

The content addressable storage system 105 in the FIG. 1 embodiment isimplemented as at least a portion of a clustered storage system andincludes a plurality of storage nodes 115 each comprising acorresponding subset of the storage devices 106. Other clustered storagesystem arrangements comprising multiple storage nodes can be used inother embodiments.

The system 100 further comprises remote storage systems 120 coupled tonetwork 104. A given such remote storage system illustratively comprisesanother instance of the content addressable storage system 105, oranother type of storage system, possibly implemented as a clusteredstorage system comprising a plurality of nodes. The given remote storagesystem is an example of what is more generally referred to herein as an“additional storage system” that participates with the contentaddressable storage system 105 in a hash-based remote rebuild assistanceprocess. It should be noted in this regard that the term “remote” asused herein, in the context of remote storage systems 120 and elsewhere,is intended to be broadly construed, and should not be interpreted asrequiring any particular geographic location relationship to the contentaddressable storage system 105. For example, the given remote storagesystem can be in a different data center than the content addressablestorage system 105, or could alternatively be at a different locationwithin the same physical site. The term “remote” in illustrativeembodiments herein can therefore simply indicate that the correspondingstorage system is physically separate from the content addressablestorage system 105.

Although multiple remote storage systems 120 are shown in the figure, itis to be appreciated that some embodiments may include only a singleremote storage system that is utilized for hash-based remote rebuildassistance.

Each of the storage nodes 115 of the content addressable storage system105 is assumed to be implemented using at least one processing devicecomprising a processor coupled to a memory.

Other arrangements of storage nodes or other types of nodes can be used.The term “node” as used herein is intended to be broadly construed and agiven such node need not include storage devices.

The storage controller 108 in this embodiment is implemented in adistributed manner so as to comprise a plurality of distributed storagecontroller components implemented on respective ones of the storagenodes 115. The storage controller 108 is therefore an example of what ismore generally referred to herein as a “distributed storage controller.”Accordingly, in subsequent description herein, the storage controller108 is more particularly referred to as a distributed storagecontroller. Other types of potentially non-distributed storagecontrollers can be used in other embodiments.

Each of the storage nodes 115 in this embodiment further comprises a setof processing modules configured to communicate over one or morenetworks with corresponding sets of processing modules on other ones ofthe storage nodes 115. The sets of processing modules of the storagenodes 115 collectively comprise at least a portion of the distributedstorage controller 108 of the content addressable storage system 105.

The modules of the distributed storage controller 108 in the presentembodiment more particularly comprise different sets of processingmodules implemented on each of the storage nodes 115. The set ofprocessing modules of each of the storage nodes 115 comprises at least acontrol module 108C, a data module 108D and a routing module 108R. Thedistributed storage controller 108 further comprises one or moremanagement (“MGMT”) modules 108M. For example, only a single one of thestorage nodes 115 may include a management module 108M. It is alsopossible that management modules 108M may be implemented on each of atleast a subset of the storage nodes 115.

Each of the storage nodes 115 of the content addressable storage system105 therefore comprises a set of processing modules configured tocommunicate over one or more networks with corresponding sets ofprocessing modules on other ones of the storage nodes. A given such setof processing modules implemented on a particular storage nodeillustratively includes at least one control module 108C, at least onedata module 108D and at least one routing module 108R, and possibly amanagement module 108M. These sets of processing modules of the storagenodes collectively comprise at least a portion of the distributedstorage controller 108.

Communication links may be established between the various processingmodules of the distributed storage controller 108 using well-knowncommunication protocols such as IP, Transmission Control Protocol (TCP),and remote direct memory access (RDMA). For example, respective sets ofIP links used in data transfer and corresponding messaging could beassociated with respective different ones of the routing modules 108R.

It is assumed in some embodiments that the processing modules of thedistributed storage controller 108 are interconnected in a full meshnetwork, such that a process of one of the processing modules cancommunicate with processes of any of the other processing modules.Commands issued by the processes can include, for example, remoteprocedure calls (RPCs) directed to other ones of the processes.

The distributed storage controller 108 of the content addressablestorage system 105 in the present embodiment is configured to providehash-based remote rebuild assistance as disclosed herein. Thedistributed storage controller 108 is assumed to comprise a type of“processing device” as that term is broadly used herein, and moreparticularly comprises at least one processor coupled to a memory.

In providing the hash-based remote rebuild assistance, the distributedstorage controller 108 in this embodiment is configured to detect adrive failure in the content addressable storage system 105.

It is assumed without limitation that the storage devices 106 of thecontent addressable storage system 105 comprise a plurality of drivesconfigured in accordance with a designated RAID configuration, such as aRAID-5 arrangement or a RAID-6 arrangement, both of which are well knownto those skilled in the art. A RAID-5 arrangement generally permitsrecovery from a single drive failure utilizing parity informationdistributed over multiple remaining drives, while a RAID-6 arrangementgenerally permits recovery from two simultaneous drive failures, alsoutilizing parity information distributed over multiple remaining drives.Illustrative embodiments are not restricted to use with RAID-5 or RAID-6arrangements, or to particular types and configurations of parityinformation that may be used in various implementations of sucharrangements.

As mentioned previously, the plurality of drives can comprise, forexample, flash drives, solid state drives, hard disk drives, hybriddrives or other types of drives, as well as combinations of differentdrives of different types. The term “drive” as used herein is thereforeintended to be broadly construed.

Also, the term “RAID” as used herein is intended to be broadlyconstrued, and should not be viewed as limited in any way to disk-baseddrives. As is well known, RAID arrangements can be implemented using awide variety of different types of storage drives.

The distributed storage controller 108 in this embodiment is furtherconfigured to identify a plurality of data pages to be rebuilt in orderto recover from the drive failure, to retrieve hash digests ofrespective ones of the identified data pages, and to utilize the hashdigests to request respective corresponding data pages from a secondstorage system.

The data pages to be rebuilt in order to recover from the drive failureare assumed to be part of one or more storage volumes of the contentaddressable storage system 105. The term “storage volume” as used hereinis intended to encompass at least one logical storage volume comprisingat least a portion of a physical storage space of one or more of thestorage devices 106 of the content addressable storage system 105.

In some embodiments, the distributed storage controller 108 utilizingthe hash digests to request respective corresponding data pages from thesecond storage system comprises the distributed storage controller 108sending multiple separate requests each including a different one of thehash digests to the second storage system. As another example, utilizingthe hash digests to request respective corresponding data pages from thesecond storage system illustratively comprises aggregating multiple onesof the hash digests into a single request that is sent to the secondstorage system. Various combinations of separate and aggregate requestscan be used in other embodiments.

The term “request” as used herein is intended to be broadly construed,and a given such request can comprise one or more messages or othertypes of communications. The request should therefore not be viewed asbeing limited to a single communication using any particular messagingprotocol.

The hash digests of the respective data pages are illustrativelygenerated by the distributed storage controller 108 prior to the drivefailure by applying a secure hashing algorithm to content of therespective data pages. More particularly, the hash digest of a givendata page can be generated by applying a secure hashing algorithm suchas SHA1 to content of the given data page in the content addressablestorage system 105. Other types of secure hashing algorithms or hashfunctions may be used. The hash digests of the respective data pages areassumed to be stored by the content addressable storage system 105 inparticular ones of the drives not utilized to store the data pages.

The second storage system is illustratively one of the remote storagesystems 120 of the information processing system 100. For example, thesecond storage system in some embodiments is an additional storagesystem configured to participate in a replication process with thecontent addressable storage system 105, and illustratively comprisesanother instance of content addressable storage system 105. Thereplication process carried out by these two storage systemsillustratively comprises at least one of a synchronous replicationprocess in which one or more storage volumes are synchronouslyreplicated from the content addressable storage system 105 to the secondstorage system, and an asynchronous replication process in which one ormore storage volumes are asynchronously replicated from the contentaddressable storage system 105 to the second storage system.

Other types of remote storage systems 120 or other additional storagesystems not necessarily participating in a replication process with thecontent addressable storage system 105 can be used. In some embodiments,the information processing system 100 is configured such that the sameor similar data is stored in the content addressable storage system 105and at least one of the remote storage systems 120 without the use ofreplication. For example, similar copies of a set of files or a databasemay be stored in the two storage systems by a given one of the hostdevices 102.

For each of one or more data pages returned by the second storagesystem, the distributed storage controller 108 utilizes the returneddata page as a rebuilt data page in recovering from the drive failure.This advantageously avoids the need for the distributed storagecontroller 108 to read multiple data pages from remaining ones of thedrives of the designated RAID arrangement in order to rebuild thatparticular returned data page.

The distributed storage controller 108 is further configured to verify agiven one of the returned data pages by computing a hash digest of thereturned data page and comparing the computed hash digest to the hashdigest utilized to request that data page from the second storagesystem.

The returned data page is considered successfully verified in someembodiments only if there is an exact match between the computed hashdigest of the returned data page and the hash digest utilized in therequest. Additional or alternative verification criteria can be used inother embodiments.

As indicated above, responsive to a successful verification, thedistributed storage controller 108 utilizes the returned data pagereceived from the additional storage system as a rebuilt data page inrecovering from the drive failure. The given data page missing as aresult of the drive failure is fully recovered by the contentaddressable storage system 105 using the returned data page, such thatthere is no need to perform a RAID recovery algorithm and its associatedread and parity computation operations for that data page. Anyassociated metadata structures are updated accordingly.

It is possible that for certain requests sent to the second storagesystem, the corresponding data page or data pages may not be availablein the second storage system. For each of one or more data pages notreturned by the second storage system responsive to a request, thedistributed storage controller 108 illustratively receives an indicationfrom the second storage system that there is no available data pagecorresponding to the hash digest in the second storage system. Theindications received from the second storage system in some embodimentsare in the form of a bitmap indicating which of the hash digests havecorresponding data pages available in the second storage system andwhich of the hash digests do not have corresponding data pages availablein the second storage system.

For each of one or more data pages not returned by the second storagesystem, the distributed storage controller 108 is configured to readmultiple data pages from remaining ones of the drives of the designatedRAID arrangement and to rebuild that data page in recovering from thedrive failure.

Accordingly, in illustrative embodiments, the distributed storagecontroller 108 responds to a detected drive failure that has resulted inmissing data pages by utilizing respective hash digests, typicallystored separately from their corresponding data pages, to request themissing data pages from the second storage system. It is expected thatmany of the requested data pages will be available in the second storagesystem, particularly if the second storage system is participating in areplication process with the content addressable storage system 105.This advantageously avoids the need to perform a time-consuming andcomputationally-intensive RAID rebuild process for any of the returneddata pages.

For example, absent use of the hash-based remote rebuild assistancefunctionality disclosed herein, the content addressable storage system105 in recovering from a drive failure using a RAID-5 or RAID-6arrangement would typically have to read multiple data pages fromremaining ones of the drives, and apply an exclusive-or (XOR) operationin order to recover a given missing data page. As a more particularexample, in a 25+1 RAID-5 arrangement with 25 data volumes and oneparity volume, suitable for recovering from a single drive failure, eachmissing page that needs to be rebuilt requires reading 25 pages from 25different drives and then computing an XOR of the 25 pages. Similarly,in a 29+2 RAID-6 arrangement with 29 data volumes and two parityvolumes, suitable for recovering from two simultaneous drive failures,rebuilding a missing data page of a failed drive requires reading 30pages from 30 different drives and then computing an XOR of the 30pages.

Illustrative embodiments avoid the need to perform these multiple readsand associated computations for any missing data pages that arerequested from and returned by the second storage system utilizing thehash digests. Instead, the returned data page is utilized to provide themissing data page. Although the normal rebuild process may in certaincases be needed for some of the missing pages, this will typically be nomore than a relatively small number of the missing pages. As a result,the number of reads and XOR computations and thus the time andcomplexity of the overall rebuild process is considerably reduced inillustrative embodiments. It was indicated above that conventionalapproaches would generally require rebuilding every single data page ofthe failed drive using a time and computation intensive RAID recoveryalgorithm, such as a RAID XOR algorithm in which multiple data pages areread from respective remaining drives and an XOR of the multiple datapages is computed. Illustrative embodiments provide a significantadvance relative to such approaches.

In some embodiments, separate instances of a request containing the hashdigest of at least one data page are sent by the content addressablestorage system 105 to each of a plurality of additional storage systems.For example, the request may be sent to multiple ones of the remotestorage systems 120 that currently participate in replication, migrationor management processes with the content addressable storage system 105or have participated in such a process at some time in the past.

The particular hash-based remote rebuild assistance operations describedabove are just examples, and additional or alternative operations can beperformed in other embodiments.

Also, one or more hash-based remote rebuild assistance operationsdescribed above as being performed by the distributed storage controller108 of the storage system 105 in other embodiments can be performed atleast in part by other storage system components under the control ofthe distributed storage controller 108, or by one of the host devices102. Also, storage controllers in other embodiments need not bedistributed over multiple nodes, but can instead be fully containedwithin a given node or other type of processing device.

Various aspects of page storage in the content addressable storagesystem 105 will now be described in greater detail. As indicated above,the storage devices 106 are configured to store metadata pages 110 anduser data pages 112, and in some embodiments may also store additionalinformation not explicitly shown such as checkpoints and write journals.The metadata pages 110 and the user data pages 112 are illustrativelystored in respective designated metadata and user data areas of thestorage devices 106. Accordingly, metadata pages 110 and user data pages112 may be viewed as corresponding to respective designated metadata anduser data areas of the storage devices 106.

The term “page” as used herein is intended to be broadly construed so asto encompass any of a wide variety of different types of blocks that maybe utilized in a block storage device of a storage system. Such storagesystems are not limited to content addressable storage systems of thetype disclosed in some embodiments herein, but are more generallyapplicable to any storage system that includes one or more block storagedevices. Different native page sizes are generally utilized in differentstorage systems of different types. For example, XtremIO™ X1 storagearrays utilize a native page size of 8 KB, while XtremIO™ X2 storagearrays utilize a native page size of 16 KB. Larger native page sizes of64 KB and 128 KB are utilized in VMAX® V2 and VMAX® V3 storage arrays,respectively. The native page size generally refers to a typical pagesize at which the storage system ordinarily operates, although it ispossible that some storage systems may support multiple distinct pagesizes as a configurable parameter of the system. Each such page size ofa given storage system may be considered a “native page size” of thestorage system as that term is broadly used herein.

A given “page” as the term is broadly used herein should therefore notbe viewed as being limited to any particular range of fixed sizes. Insome embodiments, a page size of 8 KB is used, but this is by way ofexample only and can be varied in other embodiments. For example, pagesizes of 4 KB, 16 KB or other values can be used. Accordingly,illustrative embodiments can utilize any of a wide variety ofalternative paging arrangements for organizing the metadata pages 110and the user data pages 112.

The user data pages 112 are part of a plurality of LUNs configured tostore files, blocks, objects or other arrangements of data, each alsogenerally referred to herein as a “data item,” on behalf of usersassociated with host devices 102. Each such LUN may comprise particularones of the above-noted pages of the user data area. The user datastored in the user data pages 112 can include any type of user data thatmay be utilized in the system 100. The term “user data” herein istherefore also intended to be broadly construed.

The content addressable storage system 105 is configured to generatehash metadata providing a mapping between content-based digests ofrespective ones of the user data pages 112 and corresponding physicallocations of those pages in the user data area. Content-based digestsgenerated using hash functions are also referred to herein as “hashdigests.” Such hash digests or other types of content-based digests areexamples of what are more generally referred to herein as “content-basedsignatures” of the respective user data pages 112. The hash metadatagenerated by the content addressable storage system 105 isillustratively stored as metadata pages 110 in the metadata area. Thegeneration and storage of the hash metadata is assumed to be performedunder the control of the distributed storage controller 108.

Each of the metadata pages 110 characterizes a plurality of the userdata pages 112. For example, a given set of user data pages representinga portion of the user data pages 112 illustratively comprises aplurality of user data pages denoted User Data Page 1, User Data Page 2,. . . User Data Page n.

Each of the user data pages 112 in this example is characterized by aLUN identifier, an offset and a content-based signature. Thecontent-based signature is generated as a hash function of content ofthe corresponding user data page. Illustrative hash functions that maybe used to generate the content-based signature include the above-notedSHA1 secure hashing algorithm, or other secure hashing algorithms knownto those skilled in the art, including SHA2, SHA256 and many others. Thecontent-based signature is utilized to determine the location of thecorresponding user data page within the user data area of the storagedevices 106.

Each of the metadata pages 110 in the present embodiment is assumed tohave a signature that is not content-based. For example, the metadatapage signatures may be generated using hash functions or other signaturegeneration algorithms that do not utilize content of the metadata pagesas input to the signature generation algorithm. Also, each of themetadata pages is assumed to characterize a different set of the userdata pages.

A given set of metadata pages representing a portion of the metadatapages 110 in an illustrative embodiment comprises metadata pages denotedMetadata Page 1, Metadata Page 2, . . . Metadata Page m, havingrespective signatures denoted Signature 1, Signature 2, . . . Signaturem. Each such metadata page characterizes a different set of n user datapages. For example, the characterizing information in each metadata pagecan include the LUN identifiers, offsets and content-based signaturesfor each of the n user data pages that are characterized by thatmetadata page. It is to be appreciated, however, that the user data andmetadata page configurations described above are examples only, andnumerous alternative user data and metadata page configurations can beused in other embodiments.

Ownership of a user data logical address space within the contentaddressable storage system 105 is illustratively distributed among thecontrol modules 108C.

The functionality for hash-based remote rebuild assistance in thisembodiment is assumed to be distributed across multiple distributedprocessing modules, including at least a subset of the processingmodules 108C, 108D, 108R and 108M of the distributed storage controller108.

For example, the management module 108M of the distributed storagecontroller 108 may include hash-based remote rebuild assistance controllogic that engages or otherwise interacts with corresponding controllogic instances in at least a subset of the control modules 108C, datamodules 108D and routing modules 108R in order to implement hash-basedremote rebuild assistance functionality in the content addressablestorage system 105.

In some embodiments, the content addressable storage system 105comprises an XtremIO™ storage array suitably modified to incorporatetechniques for hash-based remote rebuild assistance as disclosed herein.

In arrangements of this type, the control modules 108C, data modules108D and routing modules 108R of the distributed storage controller 108illustratively comprise respective C-modules, D-modules and R-modules ofthe XtremIO™ storage array. The one or more management modules 108M ofthe distributed storage controller 108 in such arrangementsillustratively comprise a system-wide management module (“SYM module”)of the XtremIO™ storage array, although other types and arrangements ofsystem-wide management modules can be used in other embodiments.Accordingly, functionality for hash-based remote rebuild assistance insome embodiments is implemented under the control of at least onesystem-wide management module of the distributed storage controller 108,utilizing the C-modules, D-modules and R-modules of the XtremIO™ storagearray.

In the above-described XtremIO™ storage array example, each user datapage has a fixed size such as 8 KB and its content-based signature is a20-byte signature generated using the SHA1 secure hashing algorithm.Also, each page has a LUN identifier and an offset, and so ischaracterized by <lun_id, offset, signature>.

The content-based signature in the present example comprises acontent-based digest of the corresponding data page. Such acontent-based digest is more particularly referred to as a “hash digest”of the corresponding data page, as the content-based signature isillustratively generated by applying a hash function such as the SHA1secure hashing algorithm to the content of that data page. The full hashdigest of a given data page is given by the above-noted 20-bytesignature. The hash digest may be represented by a corresponding “hashhandle,” which in some cases may comprise a particular portion of thehash digest. The hash handle illustratively maps on a one-to-one basisto the corresponding full hash digest within a designated clusterboundary or other specified storage resource boundary of a given storagesystem. In arrangements of this type, the hash handle provides alightweight mechanism for uniquely identifying the corresponding fullhash digest and its associated data page within the specified storageresource boundary. The hash digest and hash handle are both consideredexamples of “content-based signatures” as that term is broadly usedherein.

Examples of techniques for generating and processing hash handles forrespective hash digests of respective data pages are disclosed in U.S.Pat. No. 9,208,162, entitled “Generating a Short Hash Handle,” and U.S.Pat. No. 9,286,003, entitled “Method and Apparatus for Creating a ShortHash Handle Highly Correlated with a Globally-Unique Hash Signature,”both of which are incorporated by reference herein.

As mentioned previously, storage controller components in an XtremIO™storage array illustratively include C-module, D-module and R-modulecomponents. For example, separate instances of such components can beassociated with each of a plurality of storage nodes in a clusteredstorage system implementation.

The distributed storage controller 108 in this example is configured togroup consecutive pages into page groups, to arrange the page groupsinto slices, and to assign the slices to different ones of theC-modules. For example, if there are 1024 slices distributed evenlyacross the C-modules, and there are a total of 16 C-modules in a givenimplementation, each of the C-modules “owns” 1024/16=64 slices. In sucharrangements, different ones of the slices are assigned to differentones of the control modules 108C such that control of the slices withinthe distributed storage controller 108 is substantially evenlydistributed over the control modules 108C of the distributed storagecontroller 108.

The D-module allows a user to locate a given user data page based on itssignature. Each metadata page also has a size of 8 KB and includesmultiple instances of the <lun_id, offset, signature> for respectiveones of a plurality of the user data pages. Such metadata pages areillustratively generated by the C-module but are accessed using theD-module based on a metadata page signature.

The metadata page signature in this embodiment is a 20-byte signaturebut is not based on the content of the metadata page. Instead, themetadata page signature is generated based on an 8-byte metadata pageidentifier that is a function of the LUN identifier and offsetinformation of that metadata page.

If a user wants to read a user data page having a particular LUNidentifier and offset, the corresponding metadata page identifier isfirst determined, then the metadata page signature is computed for theidentified metadata page, and then the metadata page is read using thecomputed signature. In this embodiment, the metadata page signature ismore particularly computed using a signature generation algorithm thatgenerates the signature to include a hash of the 8-byte metadata pageidentifier, one or more ASCII codes for particular predeterminedcharacters, as well as possible additional fields. The last bit of themetadata page signature may always be set to a particular logic value soas to distinguish it from the user data page signature in which the lastbit may always be set to the opposite logic value.

The metadata page signature is used to retrieve the metadata page viathe D-module. This metadata page will include the <lun_id, offset,signature> for the user data page if the user page exists. The signatureof the user data page is then used to retrieve that user data page, alsovia the D-module.

Write requests processed in the content addressable storage system 105each illustratively comprise one or more 10 operations directing that atleast one data item of the content addressable storage system 105 bewritten to in a particular manner. A given write request isillustratively received in the content addressable storage system 105from a host device, illustratively one of the host devices 102. In someembodiments, a write request is received in the distributed storagecontroller 108 of the content addressable storage system 105, anddirected from one processing module to another processing module of thedistributed storage controller 108. For example, a received writerequest may be directed from a routing module 108R of the distributedstorage controller 108 to a particular control module 108C of thedistributed storage controller 108. Other arrangements for receiving andprocessing write requests from one or more host devices can be used.

The term “write request” as used herein is intended to be broadlyconstrued, so as to encompass one or more IO operations directing thatat least one data item of a storage system be written to in a particularmanner. A given write request is illustratively received in a storagesystem from a host device.

In the XtremIO™ context, the C-modules, D-modules and R-modules of thestorage nodes 115 communicate with one another over a high-speedinternal network such as an InfiniBand network. The C-modules, D-modulesand R-modules coordinate with one another to accomplish various IOprocessing tasks.

The write requests from the host devices 102 identify particular datapages to be written in the content addressable storage system 105 bytheir corresponding logical addresses each comprising a LUN ID and anoffset.

As noted above, a given one of the content-based signaturesillustratively comprises a hash digest of the corresponding data page,with the hash digest being generated by applying a hash function to thecontent of that data page. The hash digest may be uniquely representedwithin a given storage resource boundary by a corresponding hash handle.

The content addressable storage system 105 utilizes a two-level mappingprocess to map logical block addresses to physical block addresses. Thefirst level of mapping uses an address-to-hash (“A2H”) table and thesecond level of mapping uses a hash metadata (“HMD”) table, with the A2Hand HMD tables corresponding to respective logical and physical layersof the content-based signature mapping within the content addressablestorage system 105. The HMD table or a given portion thereof in someembodiments disclosed herein is more particularly referred to as ahash-to-data (“H2D”) table.

The first level of mapping using the A2H table associates logicaladdresses of respective data pages with respective content-basedsignatures of those data pages. This is also referred to as logicallayer mapping.

The second level of mapping using the HMD table associates respectiveones of the content-based signatures with respective physical storagelocations in one or more of the storage devices 106. This is alsoreferred to as physical layer mapping.

Examples of these and other metadata structures utilized in illustrativeembodiments will be described below in conjunction with FIGS. 4A through4D. These particular examples include respective A2H, H2D, HMD andphysical layer based (“PLB”) tables. In some embodiments, the A2H andH2D tables are utilized primarily by the control modules 108C, while theHMD and PLB tables are utilized primarily by the data modules 108D.

For a given write request, hash metadata comprising at least a subset ofthe above-noted tables is updated in conjunction with the processing ofthat write request.

The A2H, H2D, HMD and PLB tables described above are examples of whatare more generally referred to herein as “mapping tables” of respectivedistinct types. Other types and arrangements of mapping tables or othercontent-based signature mapping information may be used in otherembodiments.

Such mapping tables are still more generally referred to herein as“metadata structures” of the content addressable storage system 105. Itshould be noted that additional or alternative metadata structures canbe used in other embodiments. References herein to particular tables ofparticular types, such as A2H, H2D, HMD and PLB tables, and theirrespective configurations, should be considered non-limiting and arepresented by way of illustrative example only. Such metadata structurescan be implemented in numerous alternative configurations with differentarrangements of fields and entries in other embodiments.

The logical block addresses or LBAs of a logical layer of the contentaddressable storage system 105 correspond to respective physical blocksof a physical layer of the content addressable storage system 105. Theuser data pages of the logical layer are organized by LBA and havereference via respective content-based signatures to particular physicalblocks of the physical layer.

Each of the physical blocks has an associated reference count that ismaintained within the content addressable storage system 105. Thereference count for a given physical block indicates the number oflogical blocks that point to that same physical block.

In releasing logical address space in the storage system, adereferencing operation is generally executed for each of the LBAs beingreleased. More particularly, the reference count of the correspondingphysical block is decremented. A reference count of zero indicates thatthere are no longer any logical blocks that reference the correspondingphysical block, and so that physical block can be released.

It should also be understood that the particular arrangement of storagecontroller processing modules 108C, 108D, 108R and 108M as shown in theFIG. 1 embodiment is presented by way of example only. Numerousalternative arrangements of processing modules of a distributed storagecontroller may be used to implement functionality for hash-based remoterebuild assistance in a clustered storage system in other embodiments.

Additional examples of content addressable storage functionalityimplemented in some embodiments by control modules 108C, data modules108D, routing modules 108R and management module(s) 108M of distributedstorage controller 108 can be found in U.S. Pat. No. 9,104,326, entitled“Scalable Block Data Storage Using Content Addressing,” which isincorporated by reference herein. Alternative arrangements of these andother storage node processing modules of a distributed storagecontroller in a content addressable storage system can be used in otherembodiments.

As indicated previously, the host devices 102 and content addressablestorage system 105 in the FIG. 1 embodiment are assumed to beimplemented using at least one processing platform each comprising oneor more processing devices each having a processor coupled to a memory.Such processing devices can illustratively include particulararrangements of compute, storage and network resources.

The host devices 102 and the content addressable storage system 105 maybe implemented on respective distinct processing platforms, althoughnumerous other arrangements are possible. For example, in someembodiments at least portions of the host devices 102 and the contentaddressable storage system 105 are implemented on the same processingplatform. The content addressable storage system 105 can therefore beimplemented at least in part within at least one processing platformthat implements at least a one of the host devices 102.

The term “processing platform” as used herein is intended to be broadlyconstrued so as to encompass, by way of illustration and withoutlimitation, multiple sets of processing devices and associated storagesystems that are configured to communicate over one or more networks.For example, distributed implementations of the system 100 are possible,in which certain components of the system reside in one data center in afirst geographic location while other components of the system reside inone or more other data centers in one or more other geographic locationsthat are potentially remote from the first geographic location. Thus, itis possible in some implementations of the system 100 for the hostdevices 102 and the content addressable storage system 105 to reside indifferent data centers. Numerous other distributed implementations ofthe host devices 102 and/or the content addressable storage system 105are possible. Accordingly, the content addressable storage system 105can also be implemented in a distributed manner across multiple datacenters.

Additional examples of processing platforms utilized to implement hostdevices and/or storage systems in illustrative embodiments will bedescribed in more detail below in conjunction with FIGS. 5 and 6.

It is to be appreciated that these and other features of illustrativeembodiments are presented by way of example only, and should not beconstrued as limiting in any way.

Accordingly, different numbers, types and arrangements of systemcomponents such as host devices 102, network 104, content addressablestorage system 105, storage devices 106, storage controller 108 andstorage nodes 115 can be used in other embodiments.

It should be understood that the particular sets of modules and othercomponents implemented in the system 100 as illustrated in FIG. 1 arepresented by way of example only. In other embodiments, only subsets ofthese components, or additional or alternative sets of components, maybe used, and such components may exhibit alternative functionality andconfigurations.

For example, in some embodiments, at least portions of the functionalityfor hash-based remote rebuild assistance as disclosed herein can beimplemented in a host device, in a storage system, or partially in ahost device and partially in a storage system.

Illustrative embodiments are therefore not limited to arrangements inwhich all such functionality is implemented in a host device or astorage system, and therefore encompass various hybrid arrangements inwhich the functionality is distributed over one or more host devices andone or more storage systems, each comprising one or more processingdevices.

Referring now to FIG. 2, a more detailed view of a portion of thedistributed storage controller 108 in an illustrative embodiment isshown. This embodiment illustrates an example arrangement of controlmodules 108C, data modules 108D and a management module 108M of thedistributed storage controller 108. It is assumed in this embodimentthat these and possibly other modules of the distributed storagecontroller 108 are interconnected in a full mesh network, such that eachof the modules can communicate with each of the other modules, althoughother types of networks and different module interconnectionarrangements can be used in other embodiments.

The management module 108M of the distributed storage controller 108 inthis embodiment more particularly comprises a system-wide managementmodule or SYM module of the type mentioned previously. Although only asingle SYM module is shown in this embodiment, other embodiments caninclude multiple instances of the SYM module possibly implemented ondifferent ones of the storage nodes. It is therefore assumed that thedistributed storage controller 108 comprises one or more managementmodules 108M.

A given instance of management module 108M comprises hash-based remoterebuild assistance control logic 200 and associated management programcode 202. The management module 108M communicates with control modules108C-1 through 108C-x, also denoted as C-module 1 through C-module x.The control modules 108C communicate with data modules 108D-1 through108D-y, also denoted as D-module 1 through D-module y. The variables xand y are arbitrary integers greater than one, and may but need not beequal. In some embodiments, each of the storage nodes 115 of the contentaddressable storage system 105 comprises one of the control modules 108Cand one of the data modules 108D, as well as one or more additionalmodules including one of the routing modules 108R. A wide variety ofalternative configurations of nodes and processing modules are possiblein other embodiments. Also, the term “storage node” as used herein isintended to be broadly construed, and may comprise a node thatimplements storage control functionality but does not necessarilyincorporate storage devices.

The control modules 108C-1 through 108C-x in the FIG. 2 embodimentcomprise respective sets of A2H and H2D tables 204C-1 through 204C-x.The A2H tables are utilized to store address-to-hash mapping informationand the H2D tables are utilized to store hash-to-data mappinginformation, in support of mapping of logical addresses for respectivepages to corresponding physical addresses for those pages via respectivehashes or other types of content-based signatures, as described infurther detail elsewhere herein. The control modules 108C-1 through108C-x further comprise corresponding instances of hash-based remoterebuild assistance control logic 206C-1 through 206C-x that interactwith the hash-based remote rebuild assistance control logic 200 of themanagement module 108M to support hash-based remote rebuild assistanceas disclosed herein.

The control modules 108C may further comprise additional components notexplicitly shown in FIG. 2, such as respective messaging interfaces thatare utilized by the control modules 108 to generate control-to-routingmessages for transmission to the routing modules 108R, and to processrouting-to-control messages received from the routing modules 108R. Suchmessaging interfaces can also be configured to generate messages fortransmission to the management module 108M and to process instructionsand other messages received from the management module 108M.

The data modules 108D-1 through 108D-y in the FIG. 2 embodiment compriserespective control interfaces 210D-1 through 210D-y. These controlinterfaces 210D support communication between the data modules 108D andcorresponding ones of the control modules 108C. Also included in thedata modules 108D-1 through 108D-y are respective SSD interfaces 212D-1through 212D-y. These SSD interfaces 212D support communications withcorresponding ones of the storage devices 106.

The operation of the information processing system 100 will now bedescribed in further detail with reference to the flow diagram of FIG.3. The flow diagram of FIG. 3 illustrates a set of processing operationsimplementing functionality for hash-based remote rebuild assistance in acontent addressable storage system. The process includes steps 300through 316, and is suitable for use in system 100 but is more generallyapplicable to other types of storage systems in which it is desirable toprovide hash-based remote rebuild assistance in a given storage systemfrom one or more remote storage systems. The steps of the flow diagramare illustratively performed at least in part by or otherwise under thecontrol of a storage controller of a first storage system, such as thedistributed storage controller 108 of content addressable storage system105, through interaction with an additional storage system, referred toas a second storage system. The first and second storage systems in theFIG. 3 embodiment are assumed to comprise respective content addressablestorage systems that participate in a replication process, such as asynchronous or asynchronous replication process. The first and secondstorage systems can comprise respective first and second storage arrays,such as respective all-flash storage arrays implemented using sets ofdistributed storage nodes.

In step 300, the first storage system detects a drive failure andinitiates hash-based remote rebuild assistance in order to recover fromthe drive failure in a particularly efficient manner that avoids using aRAID XOR algorithm or other type of RAID recovery algorithm to rebuildat least a portion of the data pages stored on the failed drive.

Such drive failure detection can be performed at least in part by amanagement module or other processing module of a distributed storagecontroller in a clustered storage system, such as one or more of thecontrol modules 108C, data modules 108D and/or management module(s) 108Mof distributed storage controller 108 in the content addressable storagesystem 105, although other types of storage system modules or componentscan perform drive failure detection of the type disclosed herein.

In step 302, the first storage system identifies data pages to berebuilt in order to recover from the drive failure. Such data pagesillustratively comprise all of the user data pages that were stored onthe failed drive. These data pages are also referred to herein as“missing” data pages that need to be recovered.

In step 304, the first storage system retrieves hashes of respectiveones of the identified data pages and utilizes the retrieved hashes torequest corresponding data pages from the second storage system. It isassumed in the present embodiment that “hashes” refer to full hashdigests of the respective pages, although other arrangements arepossible. The hashes are typically stored separately from the data pagesin a content addressable storage system, and are therefore likely toremain available despite the drive failure.

The request referred to in step 304 can comprise a separate request foreach of the missing data pages, or one or more requests each of whichaggregates hashes for multiple ones of the missing data pages.

As an example of one possible implementation of a separate request foreach missing data page, the first storage system can proceed as follows:

1. Identify all missing data pages.

2. For each missing data page, retrieve its hash digest and send aseparate read request to the second storage system for the data pagecorresponding to this hash digest. If the hash digest exists in thesecond storage system, the second storage system returns thecorresponding data page, and otherwise returns an indication that thehash digest in the request is not recognized by the second storagesystem.

3. Repeat step 2 until all of the missing data pages are either returnedor indicated as not recognized by the second storage system.

As an example of one possible implementation of a request thataggregates hashes for multiple ones of the missing data pages, the firststorage system can combine multiple hash digests into a single readrequest that is directed to the second storage system. The secondstorage system can then respond with a bitmap indicating which of thehash digests were recognized, while also returning the correspondingdata pages.

It is assumed for the description of the FIG. 3 process that therequests for missing data pages are sent from the first storage systemonly to the second storage system, although the requests could be sentto multiple additional storage systems in other embodiments and theprocessing operations adjusted accordingly.

As indicated previously, the term “request” as used herein is intendedto be broadly construed and in some embodiments may comprise acombination of several separate communications each containing differenttypes of information. For example, a request can comprise a firstcommunication that includes a given remote rebuild assistance commandand a second separate communication that contains the hash digest of thecorresponding data page to which the remote rebuild assistance requestapplies. Numerous other multi-part or single part requests are possible.

These particular request arrangements are examples only, and other typesof requests can be used in other embodiments.

In response to receipt of a hash digest in a given request from thefirst storage system, the second storage system attempts to locate amatching hash digest. For example, in some embodiments the secondstorage system attempts to locate a matching hash digest in a PLB tablethat it maintains. If a matching hash digest is found, the secondstorage system retrieves the corresponding data page and returns it tothe first storage system as a returned data page responsive to therequest.

If a matching hash digest is not found by the second storage system, thesecond storage system provides an appropriate indication back to thefirst storage system that the corresponding data page is not availablein the second storage system. In such situations, although notexplicitly illustrated in the figure, one or more additional requestscould then be generated and sent by the first storage system to otherremote storage systems in a further attempt to locate the missing datapage not found in the second storage system.

In step 306, the first storage system receives data pages returned bythe second storage system as having respective ones of the hashesidentified in one or more requests. As it is assumed in the presentembodiment that the first and second storage systems participate in areplication process, it is highly likely that the data pages missingfrom the first storage system due to the drive failure are available inthe second storage system. Accordingly, it is expected that all or mostof the requested data pages are returned by the second storage system tothe first storage system responsive to the request.

In step 308, the first storage system computes hashes of the returneddata pages. For example, the hash digest of a given returned data pageis illustratively computed by applying a secure hashing algorithm suchas SHA1 to content of the returned data page. Other types of hashfunctions can be used to generate hash digests herein.

In step 310, a determination is made by the first storage system as towhether or not the computed hashes of the returned data pages match thehashes identified in the request. If the computed hashes for allreturned data pages match their respective hashes identified in therequest, the process moves to step 312, and otherwise moves to step 314as shown.

In step 312, the first storage system utilizes the returned data pagesas respective rebuilt data pages in recovering from the drive failure.Such an arrangement advantageously avoids the need to perform a RAID XORalgorithm or other type of RAID recovery algorithm to rebuild those datapages. This significantly improves the efficiency of the overall rebuildprocess for the missing data pages.

For example, for each missing data page that is retrieved from thesecond storage system instead of being rebuilt by the first storagesystem using a RAID XOR algorithm, a time and computation intensive partof the rebuild process (e.g., reads of multiple data pages fromrespective remaining drives, an XOR of the multiple data pages, and awrite of the rebuilt data page) with a much more efficient arrangement(e.g., read hash in first storage system, read data page from secondstorage system, write returned data page).

In step 314, the first storage system rejects any non-matching returneddata pages and rebuilds those data pages in accordance with the RAID XORalgorithm or other RAID recovery algorithm.

In step 316, the first storage system completes the recovery from thedrive failure by rebuilding any remaining data pages not returned by thesecond storage system. As noted above, it is expected that all or mostof the requested missing data pages are returned by the second storagesystem to the first storage system, as the first and second storagesystems are illustratively configured to participate in a replicationprocess. Accordingly, in some cases there may be no data pages remainingto be rebuilt in step 316.

The particular processing operations and other system functionalitydescribed above in conjunction with the flow diagram of FIG. 3 arepresented by way of illustrative example only, and should not beconstrued as limiting the scope of the disclosure in any way.Alternative embodiments can use other types of processing operations forimplementing hash-based remote rebuild assistance in a contentaddressable storage system. For example, the ordering of the processsteps may be varied in other embodiments, or certain steps may beperformed at least in part concurrently with one another rather thanserially. Also, one or more of the process steps may be repeatedperiodically, or multiple instances of the process can be performed inparallel with one another in order to support multiple instances ofhash-based remote rebuild assistance for different drive failures withina given storage system.

Functionality such as that described in conjunction with the flowdiagram of FIG. 3 can be implemented at least in part in the form of oneor more software programs stored in memory and executed by a processorof a processing device such as a computer or server. As will bedescribed below, a memory or other storage device having executableprogram code of one or more software programs embodied therein is anexample of what is more generally referred to herein as a“processor-readable storage medium.”

A storage controller such as distributed storage controller 108 that isconfigured to control performance of one or more steps of the process ofthe flow diagram of FIG. 3 in system 100 can be implemented as part ofwhat is more generally referred to herein as a processing platformcomprising one or more processing devices each comprising a processorcoupled to a memory. A given such processing device may correspond toone or more virtual machines or other types of virtualizationinfrastructure such as Docker containers or Linux containers (LXCs). Thehost devices 102 and content addressable storage system 105 of system100, as well as other system components, may be implemented at least inpart using processing devices of such processing platforms. For example,in the distributed storage controller 108, respective distributedmodules can be implemented in respective containers running onrespective ones of the processing devices of a processing platform.

As mentioned previously, the FIG. 3 process and other illustrativeembodiments herein utilizing mapping tables or other metadata structuresin implementing hash-based remote rebuild assistance.

Examples of metadata structures maintained by the first and secondstorage systems in illustrative embodiments include the A2H, H2D, HMDand PLB tables shown in respective FIGS. 4A, 4B, 4C and 4D. It is to beappreciated that these particular tables are only examples, and othertables or metadata structures having different configurations of entriesand fields can be used in other embodiments.

Referring initially to FIG. 4A, an A2H table 400 is shown. The A2H table400 comprises a plurality of entries accessible utilizing logicaladdresses denoted Logical Address 1, Logical Address 2, . . . LogicalAddress M as respective keys, with each such entry of the A2H table 400comprising a corresponding one of the logical addresses, a correspondingone of the hash handles, and possibly one or more additional fields.

FIG. 4B shows an H2D table 402 that illustratively comprises a pluralityof entries accessible utilizing hash handles denoted Hash Handle 1, HashHandle 2, . . . Hash Handle D as respective keys, with each such entryof the H2D table 402 comprising a corresponding one of the hash handles,a physical offset of a corresponding one of the data pages, and possiblyone or more additional fields.

Referring now to FIG. 4C, an HMD table 404 comprises a plurality ofentries accessible utilizing hash handles denoted Hash Handle 1, HashHandle 2, . . . Hash Handle H as respective keys. Each such entry of theHMD table 404 comprises a corresponding one of the hash handles, acorresponding reference count and a corresponding physical offset of oneof the data pages. A given one of the reference counts denotes thenumber of logical pages in the storage system that have the same contentas the corresponding data page and therefore point to that same datapage via their common hash digest. Although not explicitly so indicatedin the figure, the HMD table 404 may also include one or more additionalfields.

FIG. 4D shows a PLB table 406 that illustratively comprises a pluralityof entries accessible utilizing physical offsets denoted Physical Offset1, Physical Offset 2, . . . Physical Offset P as respective keys, witheach such entry of the PLB table 406 comprising a corresponding one ofthe physical offsets, a corresponding one of the hash digests, andpossibly one or more additional fields.

As indicated above, the hash handles are generally shorter in lengththan the corresponding hash digests of the respective data pages, andeach illustratively provides a short representation of the correspondingfull hash digest. For example, in some embodiments, the full hashdigests are 20 bytes in length, and their respective corresponding hashhandles are illustratively only 4 or 6 bytes in length.

Also, it is to be appreciated that terms such as “table” and “entry” asused herein are intended to be broadly construed, and the particularexample table and entry arrangements of FIGS. 4A through 4D can bevaried in other embodiments. For example, additional or alternativearrangements of entries can be used.

Illustrative embodiments of storage systems with hash-based remoterebuild assistance from one or more other storage systems as disclosedherein can provide a number of significant advantages relative toconventional arrangements.

For example, some embodiments provide content addressable storagesystems and other types of clustered storage systems that can quicklyrecover from drive failures by avoiding the need to perform a time andcomputation intensive RAID recovery algorithm for at least a subset ofthe data pages of the failed storage drive.

Accordingly, illustrative embodiments avoid the need to utilize the RAIDrecovery algorithm to rebuild every single data page that is missing dueto the drive failure. Such arrangements significantly reduce the amountsof time and computational resources that would otherwise be required inthe rebuild process.

Hash-based remote rebuild assistance as disclosed herein therefore alsoadvantageously reduces the vulnerability of the storage system to actualdata loss by reducing the time required to complete the rebuild process.

Furthermore, illustrative embodiments avoid the need to obtain fullcopies of one or more storage volumes impacted by the drive failure froma remote storage system.

These and other embodiments can obtain returned data pages from one ormore additional storage systems over any of a wide variety ofcommunication links. For example, returned data pages can be obtained bya given storage system from other storage systems that participate withthe given storage system in various replication, migration or managementprocesses. It is possible for the given storage system to receivereturned data pages in such embodiments even if the replication,migration or management processes are no longer active but had occurredat some point in the past.

It is to be appreciated that the particular advantages described aboveand elsewhere herein are associated with particular illustrativeembodiments and need not be present in other embodiments. Also, theparticular types of information processing system features andfunctionality as illustrated in the drawings and described above areexemplary only, and numerous other arrangements may be used in otherembodiments.

Illustrative embodiments of processing platforms utilized to implementhash-based remote rebuild assistance functionality will now be describedin greater detail with reference to FIGS. 5 and 6. Although described inthe context of system 100, these platforms may also be used to implementat least portions of other information processing systems in otherembodiments.

FIG. 5 shows an example processing platform comprising cloudinfrastructure 500. The cloud infrastructure 500 comprises a combinationof physical and virtual processing resources that may be utilized toimplement at least a portion of the information processing system 100.The cloud infrastructure 500 comprises multiple virtual machines (VMs)and/or container sets 502-1, 502-2, . . . 502-L implemented usingvirtualization infrastructure 504. The virtualization infrastructure 504runs on physical infrastructure 505, and illustratively comprises one ormore hypervisors and/or operating system level virtualizationinfrastructure. The operating system level virtualization infrastructureillustratively comprises kernel control groups of a Linux operatingsystem or other type of operating system.

The cloud infrastructure 500 further comprises sets of applications510-1, 510-2, . . . 510-L running on respective ones of theVMs/container sets 502-1, 502-2, . . . 502-L under the control of thevirtualization infrastructure 504. The VMs/container sets 502 maycomprise respective VMs, respective sets of one or more containers, orrespective sets of one or more containers running in VMs.

In some implementations of the FIG. 5 embodiment, the VMs/container sets502 comprise respective VMs implemented using virtualizationinfrastructure 504 that comprises at least one hypervisor. Suchimplementations can provide storage functionality of the type describedabove for one or more processes running on a given one of the VMs. Forexample, the given VM can implement one or more instances of the FIG. 3process for hash-based remote rebuild assistance.

An example of a hypervisor platform that may be used to implement ahypervisor within the virtualization infrastructure 504 is the VMware®vSphere® which may have an associated virtual infrastructure managementsystem such as the VMware® vCenter™. The underlying physical machinesmay comprise one or more distributed processing platforms that includeone or more storage systems.

In other implementations of the FIG. 5 embodiment, the VMs/containersets 502 comprise respective containers implemented using virtualizationinfrastructure 504 that provides operating system level virtualizationfunctionality, such as support for Docker containers running on baremetal hosts, or Docker containers running on VMs. The containers areillustratively implemented using respective kernel control groups of theoperating system. Such implementations can provide storage functionalityof the type described above for one or more processes running ondifferent ones of the containers. For example, a container host devicesupporting multiple containers of one or more container sets canimplement one or more instances of the FIG. 3 process for hash-basedremote rebuild assistance.

As is apparent from the above, one or more of the processing modules orother components of system 100 may each run on a computer, server,storage device or other processing platform element. A given suchelement may be viewed as an example of what is more generally referredto herein as a “processing device.” The cloud infrastructure 500 shownin FIG. 5 may represent at least a portion of one processing platform.Another example of such a processing platform is processing platform 600shown in FIG. 6.

The processing platform 600 in this embodiment comprises a portion ofsystem 100 and includes a plurality of processing devices, denoted602-1, 602-2, 602-3, . . . 602-K, which communicate with one anotherover a network 604.

The network 604 may comprise any type of network, including by way ofexample a global computer network such as the Internet, a WAN, a LAN, asatellite network, a telephone or cable network, a cellular network, awireless network such as a WiFi or WiMAX network, or various portions orcombinations of these and other types of networks.

The processing device 602-1 in the processing platform 600 comprises aprocessor 610 coupled to a memory 612.

The processor 610 may comprise a microprocessor, a microcontroller, anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), a graphics processing unit (GPU) or other type ofprocessing circuitry, as well as portions or combinations of suchcircuitry elements.

The memory 612 may comprise random access memory (RAM), read-only memory(ROM), flash memory or other types of memory, in any combination. Thememory 612 and other memories disclosed herein should be viewed asillustrative examples of what are more generally referred to as“processor-readable storage media” storing executable program code ofone or more software programs.

Articles of manufacture comprising such processor-readable storage mediaare considered illustrative embodiments. A given such article ofmanufacture may comprise, for example, a storage array, a storage diskor an integrated circuit containing RAM, ROM, flash memory or otherelectronic memory, or any of a wide variety of other types of computerprogram products. The term “article of manufacture” as used hereinshould be understood to exclude transitory, propagating signals.Numerous other types of computer program products comprisingprocessor-readable storage media can be used.

Also included in the processing device 602-1 is network interfacecircuitry 614, which is used to interface the processing device with thenetwork 604 and other system components, and may comprise conventionaltransceivers.

The other processing devices 602 of the processing platform 600 areassumed to be configured in a manner similar to that shown forprocessing device 602-1 in the figure.

Again, the particular processing platform 600 shown in the figure ispresented by way of example only, and system 100 may include additionalor alternative processing platforms, as well as numerous distinctprocessing platforms in any combination, with each such platformcomprising one or more computers, servers, storage devices or otherprocessing devices.

For example, other processing platforms used to implement illustrativeembodiments can comprise converged infrastructure such as VxRail™,VxRack™, VxRack™ FLEX, VxBlock™ or Vblock® converged infrastructure fromDell EMC.

It should therefore be understood that in other embodiments differentarrangements of additional or alternative elements may be used. At leasta subset of these elements may be collectively implemented on a commonprocessing platform, or each such element may be implemented on aseparate processing platform.

As indicated previously, components of an information processing systemas disclosed herein can be implemented at least in part in the form ofone or more software programs stored in memory and executed by aprocessor of a processing device. For example, at least portions of thestorage functionality of one or more components of a host device orstorage system as disclosed herein are illustratively implemented in theform of software running on one or more processing devices.

It should again be emphasized that the above-described embodiments arepresented for purposes of illustration only. Many variations and otheralternative embodiments may be used. For example, the disclosedtechniques are applicable to a wide variety of other types ofinformation processing systems, host devices, storage systems, storagenodes, storage devices, storage controllers, hash-based remote rebuildassistance processes and associated control logic. Also, the particularconfigurations of system and device elements and associated processingoperations illustratively shown in the drawings can be varied in otherembodiments. Moreover, the various assumptions made above in the courseof describing the illustrative embodiments should also be viewed asexemplary rather than as requirements or limitations of the disclosure.Numerous other alternative embodiments within the scope of the appendedclaims will be readily apparent to those skilled in the art.

What is claimed is:
 1. An apparatus comprising: at least one processingdevice comprising a processor coupled to a memory; the processing devicebeing configured: to detect a drive failure in a first storage systemcomprising a plurality of drives configured in accordance with adesignated redundant array of independent disks (RAID) arrangement; toidentify a plurality of data pages to be rebuilt in order to recoverfrom the drive failure; to retrieve hash digests of respective ones ofthe identified data pages; to utilize the hash digests to requestrespective corresponding data pages from a second storage system; andfor each of one or more data pages returned by the second storagesystem, to utilize the returned data page as a rebuilt data page inrecovering from the drive failure so as to avoid reading multiple datapages from remaining ones of the drives of the designated RAIDarrangement to rebuild that data page.
 2. The apparatus of claim 1wherein the processing device is implemented at least in part in a hostdevice configured to communicate over a network with the first andadditional storage systems.
 3. The apparatus of claim 1 wherein theprocessing device is implemented at least in part in the first storagesystem.
 4. The apparatus of claim 1 wherein the hash digests of therespective data pages are generated by the first storage system prior tothe drive failure by applying a secure hashing algorithm to content ofthe respective data pages.
 5. The apparatus of claim 1 wherein the hashdigests of the respective data pages are stored by the first storagesystem in particular ones of the drives not utilized to store the datapages.
 6. The apparatus of claim 1 wherein the processing device isfurther configured to verify a given one of the returned data pages bycomputing a hash digest of the returned data page and comparing thecomputed hash digest to the hash digest utilized to request that datapage from the second storage system.
 7. The apparatus of claim 1 whereinthe designated RAID arrangement comprises one of a RAID-5 arrangementand a RAID-6 arrangement.
 8. The apparatus of claim 1 wherein utilizingthe hash digests to request respective corresponding data pages from asecond storage system comprises sending a plurality of separate requestseach including a different one of the hash digests to the second storagesystem.
 9. The apparatus of claim 1 wherein utilizing the hash digeststo request respective corresponding data pages from a second storagesystem comprises aggregating multiple ones of the hash digests into asingle request that is sent to the second storage system.
 10. Theapparatus of claim 1 wherein the processing device is furtherconfigured, for each of one or more data pages not returned by thesecond storage system, to receive an indication from the second storagesystem that there is no available data page corresponding to the hashdigest in the second storage system.
 11. The apparatus of claim 10wherein receiving the indications from the second storage systemcomprises receiving a bitmap indicating which of the hash digests havecorresponding data pages available in the second storage system andwhich of the hash digests do not have corresponding data pages availablein the second storage system.
 12. The apparatus of claim 1 wherein theprocessing device is further configured, for each of one or more datapages not returned by the second storage system, to read multiple datapages from remaining ones of the drives of the designated RAIDarrangement to rebuild that data page in recovering from the drivefailure.
 13. The apparatus of claim 1 wherein the first storage systemis configured to participate in a replication process with the secondstorage system, the replication process comprising at least one of: asynchronous replication process in which one or more storage volumes aresynchronously replicated from the first storage system to the secondstorage system; and an asynchronous replication process in which one ormore storage volumes are asynchronously replicated from the firststorage system to the second storage system.
 14. The apparatus of claim13 wherein the storage volume comprises at least one logical storagevolume comprising at least a portion of a physical storage space of oneor more of the drives of the first storage system.
 15. A methodcomprising: detecting a drive failure in a first storage systemcomprising a plurality of drives configured in accordance with adesignated redundant array of independent disks (RAID) arrangement;identifying a plurality of data pages to be rebuilt in order to recoverfrom the drive failure; retrieving hash digests of respective ones ofthe identified data pages; utilizing the hash digests to requestrespective corresponding data pages from a second storage system; andfor each of one or more data pages returned by the second storagesystem, utilizing the returned data page as a rebuilt data page inrecovering from the drive failure so as to avoid reading multiple datapages from remaining ones of the drives of the designated RAIDarrangement to rebuild that data page; wherein the method is implementedby at least one processing device comprising a processor coupled to amemory.
 16. The method of claim 15 further comprising verifying a givenone of the returned data pages by computing a hash digest of thereturned data page and comparing the computed hash digest to the hashdigest utilized to request that data page from the second storagesystem.
 17. The method of claim 15 wherein utilizing the hash digests torequest respective corresponding data pages from a second storage systemcomprises aggregating multiple ones of the hash digests into a singlerequest that is sent to the second storage system.
 18. A computerprogram product comprising a non-transitory processor-readable storagemedium having stored therein program code of one or more softwareprograms, wherein the program code when executed by at least oneprocessing device causes said at least one processing device: to detecta drive failure in a first storage system comprising a plurality ofdrives configured in accordance with a designated redundant array ofindependent disks (RAID) arrangement; to identify a plurality of datapages to be rebuilt in order to recover from the drive failure; toretrieve hash digests of respective ones of the identified data pages;to utilize the hash digests to request respective corresponding datapages from a second storage system; and for each of one or more datapages returned by the second storage system, to utilize the returneddata page as a rebuilt data page in recovering from the drive failure soas to avoid reading multiple data pages from remaining ones of thedrives of the designated RAID arrangement to rebuild that data page. 19.The computer program product of claim 18 wherein the program code whenexecuted further causes said at least one processing device to verify agiven one of the returned data pages by computing a hash digest of thereturned data page and comparing the computed hash digest to the hashdigest utilized to request that data page from the second storagesystem.
 20. The computer program product of claim 18 wherein utilizingthe hash digests to request respective corresponding data pages from asecond storage system comprises aggregating multiple ones of the hashdigests into a single request that is sent to the second storage system.